1. Field of the Invention
The present invention relates to a high pressure fuel injection pump having a high pressure damper.
2. Description of the Related Art
The Diesel engine is well known as a direct injection type engine, into the cylinder of which fuel is directly injected. However, even a spark-ignition engine (gasoline engine), into the cylinder of which fuel is directly injected, is recently proposed. In the above engine, into the cylinder of which fuel is directly injected, it is required that a sufficiently high fuel injection pressure is provided and also a pulsation of fuel pressure is small for the purpose of stabilization of injection of fuel. For the above reasons, a single cylinder type high pressure fuel pump is commonly used, the structure of which is simple and compact and the manufacturing cost of which is low. On the other hand, since the above single cylinder type fuel injection pump has only one plunger, a pulsation of fuel pressure discharged from the fuel injection pump is considerably large. In order to absorb this pulsation of fuel pressure, there is proposed a metallic bellows type pulsation absorbing device or a diaphragm type pulsation absorbing device.
As an example of the related art, FIG. 7 shows a high pressure fuel feed pump having a high pressure damper which is a pulsation absorbing device. In FIG. 7, reference numeral 1 is a high pressure fuel feed pump, which is mounted on a housing of an engine not shown in the drawing and driven by a cam not shown in the drawing rotating at a speed of 1/2 of the engine speed. Reference numeral 2 is a casing of this high pressure fuel feed pump. Reference numeral 3 is a suction passage formed in this casing 2. Reference numeral 4 is a discharge passage formed in this casing 2 and communicated with a fuel injection valve not shown in the drawing. Reference numeral 5 is a drain passage formed in the above casing 2.
Reference numeral 6 is an accommodating recess formed at a lower end portion of the above casing 2. This accommodating recess 6 includes a screw portion 6a and a bottom portion 6b. Reference numeral 7 is an accommodating recess formed at an upper end portion of the above casing 2. This accommodating recess 7 includes a screw portion 7a. Reference numeral 8 is an accommodating recess formed at a right end portion of the above casing 2.
Reference numeral 9 is a sleeve arranged in the accommodating recess 6 of the above casing 2. The sleeve 9 is composed of a cylinder portion 9a and a fixing portion 9b formed into a flange-shape. Reference numerals 10 and 11 are respectively a plate A and a plate B arranged between a bottom portion 6b of the accommodating recess 6 of the casing 2 and the sleeve 9. A reed valve 12 is interposed between these plates A and B.
On each of the above plates A and B, there are formed a suction hole communicating with the suction passage 3, a discharge hole communicating with the discharge passage 4, and a drain hole communicating with the drain passage 5. On the other hand, in the reed valve 12, there are provided a suction valve, a discharge valve which make fuel pass in one direction, and a drain hole, wherein the suction valve and the discharge valve are respectively located at positions corresponding to the suction hole and the discharge hole.
Reference numeral 13 is a cylindrical piston reciprocatingly arranged in a cylinder portion 9a of the sleeve 9. The cylindrical piston 13 forms a fuel pressurizing chamber 14 together with the cylinder portion 9a. Reference numeral 15 is a compression coil spring arranged in the fuel pressurizing chamber 14. Reference numeral 16 is a spring holder for positioning the compression coil spring 15.
Reference numeral 17 is a housing arranged round the sleeve 9 in such a manner that the housing surrounds the sleeve 9. The housing 17 is formed into a substantial bowl shape having no bottom. At the outer circumferential portion of the housing 17, there is provided a cylindrical edge portion 17a. Reference numeral 18 is a holder fixed at an end portion of the piston 13 on the opposite side of the fuel pressurizing chamber 14. Reference numeral 19 is a bellows made of metal arranged between the holder 18 and the housing 17. When fuel has leaked out from between the piston 13 and the sleeve 9, the fuel is accommodated inside the bellows 19.
Reference numeral 20 is a tappet attached to an end portion of the piston 13 on the opposite side of the fuel pressurizing chamber 14. The tappet 20 is driven by a cam not shown in the drawing.
Reference numeral 21 is a bracket for fixing the high pressure fuel pump 1 to a housing and others of an engine not shown in the drawing. Reference numeral 22 is a clamp screw fastened to the screw portion 6a of the casing 2. The housing 17, sleeve 9, plate A 10, plate B 11 and reed valve 12 are pushed and fixed to a bottom portion of the accommodating recess 6 by the clamp screw 22.
Reference numeral 23 is a heat insulating plate attached to the bracket 21. The pump body 24 of the high pressure fuel feed pump is composed of the above components from the sleeve 9 to the heat insulating plate 23.
Reference numeral 25 is a high pressure damper attached to the accommodating recess 7 of the casing 2. The high pressure damper 25 is communicated with the discharge passage 4 on the high pressure side and composes a high pressure accumulator which is a pulsation absorbing device of fuel. Reference numeral 26 is a high pressure container. Reference numeral 27 is a plate accommodated in a bottom portion of the accommodating recess 7 of the casing 2. Reference numeral 28 is a thin flexible disk-shaped diaphragm made of metal which forms a high pressure chamber 29 in cooperation with the case 26. A circumferential edge portion of the diaphragm 28 is interposed between the case 26 and the plate 27 so that the circumferential edge portion can be sealed.
Reference numeral 30 is a ring-shaped clamp screw and fastened to the screw portion 7a of the casing 2, so that the case 26, diaphragm 28 and plate 27 are pushed and fixed to a bottom portion of the accommodating recess 7 by the clamp screw 30.
Reference numeral 31 is a low pressure damper attached to the accommodating recess 8 of the casing 2. The low pressure damper 31 is communicated with the suction passage 3 on the low pressure side, so that the pulsation of fuel can be absorbed by the low pressure damper 31. Reference numeral 32 is a cylindrical housing attached to a bottom portion of the accommodating recess 8 of the casing 2. Reference numeral 33 is a lid to tightly close up this housing. Reference numeral 34 is a bellows, one side of which is fixed to this lid 33.
In the high pressure fuel injection pump composed as described above, the piston 13 is pushed to the tapper 20 side by the compression coil spring 15. The tappet 20 is driven by a cam driven by an engine. By transmitting a force from the rotation of the cam, and the piston 13 is reciprocated in the cylinder portion 9a.
When the piston 13 is lowered, fuel is sucked from the suction passage 3 into the fuel pressurizing chamber 14 via the reed valve 12. When the piston 13 is raised, a suction valve of the reed valve 12 is closed. On the other hand, the discharge valve is opened, so that fuel in the fuel pressurizing chamber 14 is discharged from the discharge passage 4. Fuel, which has leaked out from between the piston 13 and the sleeve 9, is stored inside the bellows 19 and returned to a fuel tank not shown via the drain passage 5.
In the apparatus of the related art described above, in order to seal up the end surface of the sleeve 9, plate A, plate B, reed valve 12 and casing 2, the clamp screw 22 is fastened with respect to the pump body 24 by a clamping force not lower than 2000 kg, so that the sealing property can be provided. Also, in order to tightly attach the high pressure damper 25 to the pump body 24, the clamp screw 30 is fastened by a clamping force not lower than 2000 kg.
However, as shown in FIG. 8, an attaching center of the pump body 24 and an attaching center of the high pressure damper 25 are offset to each other, in view of the arrangement of the fuel passage and the thickness of the casing 2. Therefore, when the high pressure damper 25 is fastened to the casing 2, a force is given to the casing 2 as shown by a broken line in FIG. 8. Accordingly, a portion to which the plate of the pump body 24 is attached is deformed upward. Therefore, gaps are formed among plate A, plate B and casing 2. As a result, fuel leaks from these gaps, and the pump efficiency is deteriorated.
The surface of the casing 2 onto which the pump body 24 is attached is machined by means of cutting. Accordingly, as shown in FIGS. 9 and 10, the cutting grooves become communicating passages, and the low pressure passage and the high pressure passage are communicated with each other, that is, fuel leaks from the cutting grooves and the pump efficiency is lowered.
Further, when a gap is formed between plate A and plate B, abrasion is caused on the plates and the durability is deteriorated.